The invention relates to a hydraulic switching device.
European patent document EP 0 656 274 B1 discloses a circuit that can pressurize four outlets U1 to U4 with a pressure medium in different ways using a design of two controllable selector switches, namely, on the one hand, a reversing switch for controlling direction of pump rotation, and, on the other hand, an electro-motorized movable control valve. Due to the symmetry of the arrangement, switch conditions of the outlets are limited to a certain degree: if the first outlet is pressurized, only one selection capability remains for pressurizing the other outlets with a pressure medium. For example, if an outlet designated with U1 is pressurized (cf. FIG. 1), then the only available selection is, whether outlet line U3 shall be pressurized or if this line shall be switched pressure-less. In either case, outlets U2 and U4 will be pressure-less.
If there are more than four outlets, the problem remains that only one outlet strand can be pressurized at a time corresponding to the direction of rotation of the motor. This limits the application capabilities of such circuits. In addition, reversing the motor""s direction of rotation takes a relatively long time and can be initiated only once a preceding movement phase has been concluded.
The object of the invention is to remove the above noted disadvantages without using additional electrically controllable selector switches.
A switching device of the present invention comprises a first drive unit, for example, a hydraulic cylinder or a pair of hydraulic cylinders, can be pressurized in one direction of movement, here in the counter direction. The second drive unit, for example, an additional hydraulic cylinder, has another three selection capabilities for pressurization: the direction of the function, the counter direction or a force-free switching. This results in a more favorable distribution of the switching capabilities with the same amount of electrically controllable selector switches such that new application capabilities are created.
A pump with one direction of rotation is used so that a second electrical control for selecting the pump""s direction of rotation is dispensable. Furthermore, various pump types can be used while the pump selection is limited for reversible pumps. The breaks in movement when reversing the direction of the motor are thus eliminated. In addition, movement phases can overlap; for example, with a convertible vehicle, the soft top compartment cover can be moved during the opening of the bracket. The overall movement is faster.
By doing without the selector switch for reversing the pump direction, an additional 3/2-type valve, for example, can be used in the switching device while maintaining the expenditure in the electrical circuitry.
A particular simplification is achieved when, for example, with simultaneous pressurization of the connecting lines on both the piston rod side and the piston head side, an introduction of force is achieved that causes the piston rod to extend, because the cross-section on the side of the piston rod is smaller than that on the side of the piston head. In this case, when switching from retracting the piston (here considered the functional direction) to extending the piston (here considered the counter-direction), a reversal of the connecting line at the piston rod side can be avoided; only the connection on the piston head side needs to be pressurized.
The switching device finds a particular advantageous use in a convertible vehicle, where with a closed top, a bracket at the end of the soft top can be pressurized both in the opening and in the closing direction in order to enable the opening of the soft top compartment cover in the opening phase while it can be placed on top of it after closing the soft top compartment cover in the closing phase. In addition, the bracket must be switched pressure-less during the opening phase of the soft top. Thus, the second drive unit requires a total of three switch conditions and the first drive unit one switch condition, whereas during the switching of the first drive unit in the direction of opening the soft top, the drive for the bracket is to be kept pressure-less.
Additional advantages and features will become apparent from a first exemplary embodiment, where two drive units are interconnected, and from a second exemplary embodiment, where three drive units are interconnected.